This invention is directed to novel antenna structures and systems including an antenna array for both transmit (Tx) and receive (Rx) operations.
In communications equipment such as cellular and personal communications service (PCS), as well as multi-channel multi-point distribution systems (MMDS) and local multi-point distribution systems (LMDS) it has been conventional to receive and retransmit signals from users or subscribers utilizing antennas mounted at the tops of towers or other structures. Other communications systems such as wireless local loop (WLL), specialized mobile radio (SMR) and wireless local area network (WLAN) have signal transmission infrastructure for receiving and transmitting communications between system users or subscribers which may also utilize various forms of antennas and transceivers.
All of these communications systems require amplification of the signals being transmitted and received by the antennas. For this purpose, it has heretofore been the practice to use conventional linear power amplifiers, wherein the cost of providing the necessary amplification is typically between U.S. $100 and U.S. $300 per watt in 1998 U.S. dollars. In the case of communications systems employing towers or other structures, much of the infrastructure is often placed at the bottom of the tower or other structure with relatively long coaxial cables connecting with antenna elements mounted on the tower. The power losses experienced in the cables may necessitate some increase in the power amplification which is typically provided at the ground level infrastructure or base station, thus further increasing expense at the foregoing typical costs per unit or cost per watt.
Moreover, conventional power amplification systems of this type generally require considerable additional circuitry to achieve linearity or linear performance of the communications system. For example, in a conventional linear amplifier system, the linearity of the total system may be enhanced by adding feedback circuits and pre-distortion circuitry to compensate for the nonlinearities at the amplifier chip level, to increase the effective linearity of the amplifier system. As systems are driven to higher power levels, relatively complex circuitry must be devised and implemented to compensate for decreasing linearity as the output power increases.
Output power levels for infrastructure (base station) applications in many of the foregoing communications systems is typically in excess of ten watts, and often up to hundreds of watts which results in a relatively high effective isotropic power requirement (EIRP). For example, for a typical base station with a twenty watt power output (at ground level), the power delivered to the antenna, minus cable losses, is around ten watts. In this case, half of the power has been consumed in cable loss/heat. Such systems require complex linear amplifier components cascaded into high power circuits to achieve the required linearity at the higher output power. Typically, for such high power systems or amplifiers, additional high power combiners must be used.
All of this additional circuitry to achieve linearity of the overall system, which is required for relatively high output power systems, results in the aforementioned cost per unit/watt (between $100 and $300).
The present invention proposes distributing the power across multiple antenna (array) elements, to achieve a lower power level per antenna element and utilize power amplifier technology at a much lower cost level (per unit/per watt).
In accordance with one aspect of the invention a distributed antenna device comprises a plurality of transmit antenna elements, a plurality of receive antenna elements and a plurality of power amplifiers, one of said power amplifiers being operatively coupled with each of said transmit antenna elements and mounted closely adjacent to the associated transmit antenna element, such that no appreciable power loss occurs between the power amplifier and the associated antenna element, at least one of said power amplifiers comprising a low noise amplifier and being built into said distributed antenna device for receiving and amplifying signals from at least on of said receive antenna elements, each said power amplifier comprising a relatively low power, relatively low cost per watt linear power amplifier chip.